Driving low voltage brushless direct current (BLDC) three phase motors from higher voltage sources

ABSTRACT

A control method for a sensor-less, brushless, three-phase DC motor. The stator coil in the electromagnets inside the motor may be used as the inductive element through which a voltage regulator can regulate the current as a means of regulating the output voltage. The value of the control signal provided to the drivers controlling power to the coils may be calculated based on at least the rail voltage, as measured in real time. This allows for a wide variation of input voltages, while maintaining a relatively constant output power to the motor. In general, by taking into account the value of the rail voltage when determining the final value of the control signal that is applied to the stator coils, the maximum current through the stator coils may be scaled to the same magnitude current that would be expected to flow through the coils if the rail voltage were the rated (nominal) fan/motor voltage, even when the actual rail voltage is different, e.g. higher than the rated fan/motor voltage.

INCORPORATION BY REFERENCE

U.S. patent application Ser. No. 12/393,996, titled “Brushless, ThreePhase Motor Drive”, filed Feb. 26, 2009 and whose inventors are Lynn R.Kern and James P. McFarland; U.S. provisional application Ser. No.61/108,320 titled “Sensor-less, Brushless, Three Phase Motor Drive”,filed on Oct. 24, 2008 and whose inventor is Lynn R. Kern; U.S. patentapplication Ser. No. 12/620,726, titled “Brushless, Three Phase MotorDrive”, filed Nov. 18, 2009 and whose inventors are Lynn R. Kern, ScottC. McLeod, and Kenneth W. Gay; and U.S. patent application Ser. No.12/632,495, titled “Drive Method to Minimize Vibration and Acoustics InThree Phase Brushless DC (TPDC) Motors”, filed Dec. 7, 2009 and whoseinventors are Lynn R. Kern and James P. McFarland are all herebyincorporated by reference in their entirety as though fully andcompletely set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to DC (Direct Current) motors used invarious applications, such as hard disk drive motors, cooling fans,drive motors for appliances, etc.

2. Description of the Related Art

Electric motors are used to produce mechanical energy from electricalenergy, used in a number of applications, including different householdappliances, pumps, cooling fans, etc. Electric motors are generallyclassified as either alternating current (AC) motors or direct current(DC) motors.

Motors generally include a rotor, which is the non-stationary (moving)part of the motor, and a stator, which is the stationary part of themotor. The stator generally operates as a field magnet (e.g.,electromagnet), interacting with an armature to induce motion in therotor. The wires and magnetic field of the motor (typically in thestator) are arranged so that a torque is developed about the rotor'saxis, causing rotation of the rotor. A motor typically also includes acommutator, which is an electrical switch that periodically reverses thecurrent direction in the electric motor, helping to induce motion in therotor. The armature carries current in the motor and is generallyoriented normal to the magnetic field and the torque being generated.The purpose of the armature is to carry current crossing the magneticfield, thus creating shaft torque in the motor and to generate anelectromotive force (EMF).

In a typical brushed DC motor, the rotor comprises one or more coils ofwire wound around a shaft. Brushes are used to make mechanical contactwith a set of electrical contacts (called the commutator) on the rotor,forming an electrical circuit between the DC electrical source and thearmature coil-windings. As the armature rotates on an axis, thestationary brushes come into contact with different sections of therotating commutator. The commutator and brush system form a set ofelectrical switches, each firing in sequence, such that electrical-poweralways flows through the armature coil closest to the stationary stator(permanent magnet). Thus an electrical power source is connected to therotor coil, causing current to flow and producing electromagnetism.Brushes are used to press against the commutator on the rotor andprovide current to the rotating shaft. The commutator causes the currentin the coils to be switched as the rotor turns, keeping the magneticpoles of the rotor from ever fully aligning with the magnetic poles ofthe stator field, hence maintaining the rotation of the rotor. The useof brushes creates friction in the motor and leads to maintenance issuesand reduced efficiency.

In a brushless DC motor, the commutator/brush-gear-assembly (which iseffectively a mechanical “rotating switch”) is replaced by an externalelectronic switch that's synchronized to the rotor's position. BrushlessDC motors thus have an electronically controlled commutation system,instead of a mechanical commutation system based on brushes. In abrushless DC motor, the electromagnets do not move, but rather thepermanent magnets rotate and the armature remains static. This avoidsthe problem of having to transfer current to the moving armature.Brushless DC motors offer a number of advantages over DC motorsfeaturing brushes, including higher efficiency and reliability, reducednoise, longer lifetime (no brush erosion), the elimination of ionizingsparks from the commutator, and overall reduction of electromagneticinterference (EMI).

One issue oftentimes taken into consideration when designing motors,more specifically brushless motors, is the power required to operate themotor. One technique to reduce power in some applications has been theintroduction of Three Phase Brushless DC (TPDC) Motors. Such motors areused in a variety of applications, for example in driving cooling fans.However, in certain cooling applications the desired power is not alwaysavailable, oftentimes requiring the use of a non-ideal regulator toreduce the available voltage level to a level useable by the fan beingdriven by the motor. For example, a regulated voltage in the 5V DC to 12V DC range may need to be derived from a 9V DC to 21V DC voltageprovided by a battery in portable applications, or from a 20V DC to 48VDC voltage available in industrial applications. Because regulators aretypically not 100% efficient, the efficiencies of all regulators betweenthe source and point of use have to be multiplied to obtain an overallefficiency. Efficient switching step-down regulators, commonly known as“buck” regulators are widely used, and typically operate at 95%efficiency. If two regulators of this type are used in series, overallefficiency decreases to 90%.

Most current solutions are limited to developing very efficient buckregulators capable of high input voltages at relatively low current, andproducing low voltage, high current outputs. Buck regulators canregulate current through an inductive element as a means of regulatingoutput voltage. One method of implementing this control method is to usea fixed frequency PWM signal, and vary duty cycle based on load tomaintain constant current. While such a control method can result in avery efficient voltage regulator, the efficiency of the regulator willhave to be multiplied with the efficiency of the motor driver drivingthe fan to determine the overall electrical efficiency of the entirecooling subsystem. Anything less than 100% efficiency results in energybeing lost in the conversion from one rail voltage to another. Furtherlosses are encountered during the commutation process, as there arefinite losses in the switching transistors that may be used incommutation. For example, a very efficient buck regulator—running at 95%efficiency—driving a motor driver that is 90% efficient would yield anoverall electrical efficiency of 85.5%. In many cases this wouldrepresent less than the desired efficiency.

Other corresponding issues related to the prior art will become apparentto one skilled in the art after comparing such prior art with thepresent invention as described herein.

SUMMARY OF THE INVENTION

Various embodiments are presented of a system and method for controllinga brushless three-phase DC motor. The motor may be an electronic motor,and may include a rotor having one or more permanent magnets. The one ormore permanent magnets may be physically positioned in-board orout-board of the stationary section of the motor, referred to as thestator, which may include a plurality of electromagnets. The motor mayinclude a voltage sensor configured to measure a voltage induced acrossone or more of the electromagnets. The voltage sensor may be part of theelectromagnet. Each electromagnet may include such a voltage sensor, oralternatively, a voltage sensor may be used to measure voltage for someor all of the electromagnets. Alternatively, the motor may comprise oneor more Hall sensors or other equivalent sensors for measuring voltage.

The system may include logic for controlling the operation of the motor.The logic may be analog or digital, e.g., the logic may include one ormore state machine based controllers or one or more application specificintegrated circuits. The motor may instead (or in addition) include aprocessor, such as a microcontroller, and a computer accessible memorymedium storing program instructions executable to control the motor. Theprocessor may be configured to execute program instructions from thememory medium to control the motor.

The logic may be configured to iteratively perform certain steps. Apulse-width modulation (PWM) duty cycle may be calculated based on aminimum duty cycle and an input command. The input command may bescalable from the minimum duty cycle to a maximum duty cycle. The inputcommand may be updatable at an adjustable interval, such as a number ofiterations of the method, or an amount of time. The adjustable intervalmay be adjusted based on either 1) a number of intervals that haveoccurred since initiation (e.g. an initial iteration) of the method, or;2) an amount of time that has occurred since initiation of the method;or 3) an estimated or calculated speed of the motor.

A voltage may be measured at a first expected zero crossing value. Inone embodiment, the voltage induced by rotation of the rotor may besampled at a first expected zero crossing value. The voltage may beinduced across an undriven electromagnet of the plurality ofelectromagnets. Sampling this induced voltage may produce a firstsampled voltage value. An average of a plurality of sampled voltagevalues may then be calculated. The plurality of sampled voltage valuesmay include voltage values sampled at a plurality of prior expected zerocrossing values and the first sampled voltage. The first sampled voltagevalue may then be subtracted from the calculated average to produce adelta zero crossing error.

The delta zero crossing error may be multiplied by a first constant toproduce a representation of an angular velocity, where the firstconstant may represent electromechanical properties of the motor. Therepresentation of the angular velocity may be divided by secondconstant, then be truncated, e.g. to an integer value. One or more timevalues may then be generated based on the representation of the angularvelocity. The one or more time values may include a period, e.g., anamount of time until a next commutation of the plurality ofelectromagnets. The one or more time values may indicate a next expectedzero crossing value. The next expected zero crossing value may be thesame time value as the next commutation time of the plurality ofelectromagnets, or they may be different time values.

Operation of the motor may then be controlled based on the one or moretime values and the PWM duty cycle. More specifically, the plurality ofelectromagnets on the stator may be driven by periodic bursts of currentwhose frequency and power may be specified by the PWM duty cycle in sucha way as to drive the rotor at a particular rotational speed, while theone or more time values may determine the commutation timing of theelectromagnets on the stator, such that the electromagnetic field of thestator may remain substantially in optimal alignment with the rotor,effecting an efficient transfer of power to the rotor at that particularrotational speed.

The above operations may repeat over a plurality of iterations. In oneembodiment, the next zero crossing value from the previous iteration isused as the first expected zero crossing value in the next iteration. Inone set of embodiments, the stator coil in the respective electromagnetson the stator is used as the inductive element that a regulator, such asa buck regulator can use to regulate the current. While a regulator maytypically regulate the current in the inductive element as a means ofregulating the output voltage, in various embodiments disclosed herein,such regulators may be used specifically with the intent of regulatingthe current in the stator coils, without any intent of regulating theoutput voltage. The duty cycle to the coils may then be calculated basedon both the input command, and the rail voltage used for powering thedrivers that drive the plurality of electromagnets, as measured in realtime. This allows for wide variation of input voltage, while maintaininga relatively constant output power to the motor drive. Thus, in additionto basing the final PWM duty cycle on the input command, anothervariable, the rail voltage may also be used to scale the final PWM dutycycle that is applied to the stator coils, to effectively scale themaximum current through the stator coils to the same magnitude currentthat would be expected to flow through the coils if the rail voltagewere the rated (nominal) fan voltage, and not the actual rail voltage.

Thus, in one set of embodiments, a rotating motor—which includes a setof electromagnets, with each electromagnet having a respective coil—maybe controlled by first inducing a respective current in one or more ofthe respective coils, using a regulated output voltage derived from asupply voltage, and issuing an input command to adjust a speed ofrotation of the rotating motor to a desired base value. In addition, thevalue of a control signal may be determined based on the input commandand the value of the supply voltage, and the induced respective currentin one or more of the respective coils may be adjusted to a desiredrespective value using the control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate different views of an exemplary fan and fanmotor;

FIG. 2 illustrates a simplified diagram of one embodiment of a brushlessfour-pole three-phase electric motor;

FIG. 3 illustrates the commutation pattern of a brushless three-phaseelectric motor according to one embodiment;

FIG. 4 is a circuit diagram of one embodiment of a motor with HallSensors and Hall Sense amplifiers;

FIG. 5 is a circuit diagram of one embodiment of a motor with drivecontrol logic; and

FIG. 6 is shows a simplified block diagram of another embodiment of arotating motor and control circuitry to control a speed of rotation ofthe motor.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIGS. 1A and 1B—Exemplary Fan and Fan Motor

FIGS. 1A and 1B illustrate an exemplary fan assembly 110 according toone embodiment. Fan 110 may be a cooling fan, for example a fan for usein a laptop or a desktop computer. Fan 110 may alternatively be acommercial or industrial fan, or in general any type of fan driven by amotor. Fan assembly 110 may include a motor assembly 100 as well as fanblades 120. Motor assembly 100 may comprise a motor (e.g. motor 102shown in FIG. 5) as well as drive circuitry (for example, drive controllogic 502 shown in FIG. 5) for controlling motor 102.

Although FIGS. 1A and 1B illustrate a fan as the load being driven bythe motor, it should be noted that the system and method for controllinga motor as described herein may be suited for driving any of varioustypes of loads, including without limitation hard disk drives, drivemotors for appliances, propellers, wheels, pumps, or other loads.

FIG. 2—Brushless Four-Pole Three-Phase Motor

FIG. 2 illustrates a simplified diagram of an exemplary brushlessfour-pole three-phase motor 102. Motor 102 may be electrically powered,e.g., by direct current (DC) electricity. Motor 102 may also beelectronically controlled, and may include a rotor 202, which mayinclude one or more permanent magnets Rotor 202 may have four poles asshown, with alternating North “N” and South “S” poles. Alternatively,rotor 202 may include two, six or any other number of poles as desired.Motor 102 may include a stator 204 including a plurality ofelectromagnets 206, positioned around rotor 202. There may be sixelectromagnets 206, which may be arranged such that they are equallyspaced with respect to each other around stator 204. Electromagnets 206may be arranged as three pairs of electromagnets 206, such that eachpair of electromagnets may be powered in a different phase than theother (remaining) pairs of electromagnets. The three pairs ofelectromagnets 206 may be connected in a “Y” configuration, making motor102 a three-phase motor. Motor 102 may be brushless, e.g., it may notinclude any brushes relaying current to rotor 202. Additionally, motor102 may be sensor-less, e.g. it may not include a discrete rotorposition sensing mechanism such as one or more Hall sensors (e.g. theHall sensors shown in FIG. 4). In another embodiment, motor 102 mayinclude Hall sensors. Two of the three pairs of electromagnets 206 onstator 204 may be driven to induce or maintain rotation of rotor 202 atany given time. Motor 102 may then utilize one of the undrivenelectromagnets of stator 204 to indirectly detect the position of rotor202 (or it may use Hall sensors for detection). The phases of stator 204may be driven in a pattern ideally configured to induce rotation ofrotor 202. The polarity of electromagnets 206 may be periodicallycommutated as part of this pattern.

FIG. 3—Commutation Pattern of a Brushless Three-Phase Motor

FIG. 3 illustrates a simplified circuit diagram depicting a commutationpattern of a brushless three-phase motor according to one embodiment.Motor 102 may be a brushless, three-phase DC motor as described above.Electromagnets 206 may be connected in a “Y” configuration as shown.Motor 102 may also be a sensor-less motor as also described above, e.g.it may utilize an undriven stator electromagnet to indirectly detect theposition of the rotor. In alternate embodiments, motor 102 may includeHall sensors to detect the position of rotor 202. Motor 102 maydetermine the timing of each commutation of the commutation patternaccording to one embodiment of a method described herein. To controlrotation of rotor 202, two pairs of the electromagnets on stator 204 maybe driven at any one time. A given pair may be driven on the ‘high-side’or the ‘low-side’, indicating in which direction current is beingconducted in the windings of the driven pair of electromagnets.Depending on the number of poles in rotor 202, the electromagnets of agiven pair of electromagnets may be wound in the same direction or inopposite directions. For example, with a four-pole rotor (as shown inFIG. 2), the windings may be configured such that the opposite sides ofan electromagnet pair may present the same polarity (e.g., ‘S’) to therotor, while with a two pole rotor, the windings may be configured suchthat the opposite sides may present opposing polarity (e.g., one ‘S’,one ‘N’). Thus in some cases the convention used to define thepolarities indicated by ‘high-side’ and ‘low-side’ may depend on themagnetic configuration of rotor 202. Other naming and/or drivingconventions are also possible and are contemplated.

A commutation cycle may include six phases. The phases may correspond tothe numbered arrows (‘1’ through ‘6’) shown in FIG. 3. In FIG. 3, eacharrow points from the high-side driven pair to the low-side driven pair.Thus for example, arrow ‘1’ may indicate that in the first phase of thecommutation cycle, ‘U’ electromagnet pair 302 may be driven on thehigh-side, while ‘V’ electromagnet pair 304 may be driven on thelow-side, with ‘W’ electromagnet pair 306 remaining undriven. Arrow ‘2’may then indicate that in the second phase of the commutation cycle, ‘U’electromagnet pair 306 may again be driven on the high-side, while ‘W’electromagnet pair 304 may be driven on the low-side, with ‘V’electromagnet pair 302 remaining undriven. Each of the remainingnumbered phases (illustrated by arrows ‘3’ through ‘6’) would operate ina similar manner to create a full commutation cycle, which may berepeated to increase, maintain, or otherwise affect rotation of rotor202.

If motor 102 is a DC powered motor, rotational speed may be controlledby means of pulse width modulation (PWM) of the electromagnets.Generally speaking, a PWM duty cycle may indicate how fast rotor 202should rotate. More specifically, the PWM duty cycle may specify howoften and with how much power to drive electromagnets 206 of stator 202.

As noted above, one pair of electromagnets may remain undriven duringeach phase of the commutation cycle. If rotor 202 is rotating, themovement of the one or more permanent magnets in rotor 202 past theundriven electromagnet may cause an induced voltage in the undrivenelectromagnet. Thus, during each phase of the commutation cycle,whichever pair of electromagnets is undriven may be used to sample thevoltage induced by the rotation of the permanent magnet(s) in rotor 202in one or both of those electromagnets. This is also known as BackElectro-Motive Force (BEMF) sampling. The sampled voltage may be used tohelp determine the present position and/or rotational velocity of rotor202. The sampled voltage or information inferred from the sampledvoltage may be used to control future commutation timing and/or otheraspects of motor control according to various embodiments. As notedabove, embodiments in which motor 102 includes Hall elements (i.e. Halleffect sensors) to detect the absolute position of the rotor, BEMFsampling may not be required, and therefore may not be used.

FIG. 4—Circuit Diagram of a Motor with Hall Sensors and Hall Senseamplifiers

As mentioned above, some motors may include Hall elements (or sensors)to detect the position of rotor 202. FIG. 4 illustrates a simplifiedcircuit diagram depicting brushless DC motor 400 that includes Halleffect sensors 402 a-402 c. One advantage of brushless motors in generalis the reduction in the power required to operate the motor. FIG. 4 isillustrative of one embodiment of a typical three-phase brushless DC(TPDC) motor. The drive electronics for motor 400 rely on Hall elements(Hall effect sensors) 402 a-402 c to detect the absolute position of therotor at all times, and switch drive transistors (404 a-404 c) tomaintain motor rotation. A Hall effect sensor may be a transducer thatvaries its output voltage in response to changes in magnetic field.Motor 400 may be electrically connected in a “Y” configuration as shown(and as also previously mentioned), so named due to the configuration'sresemblance to the letter “Y”. A common point for the three coils 404a-404 c may be connected to the electrical source VDD, and driveelectronics 410 may be operated to switch drive transistors 404 a-404 cto maintain the rotating electro-magnetic field required to turn motor400.

FIG. 5—Circuit Diagram of a Motor with Drive Control Logic

FIG. 5 illustrates a simplified circuit diagram of a motor 500 (whichmay be similar to motor 102 shown in FIG. 2), and its drive controllogic 502. In contrast to motor 400 shown in FIG. 4, motor 500 may usesix drive transistors, as shown in FIG. 5. In this configuration, onehigh-side pair of electromagnets and one low-side pair of electromagnetsmay be on at any point in time, completing the electrical circuitthrough two of the three legs (of the Y configuration) of the motor. Aspreviously mentioned, in this case the un-energized coil may be used asa magnetic sensor to determine the rotor position, referred to as BEMFdetection. The motor system shown in FIG. 5 therefore has the addedbenefit of eliminating the relatively expensive Hall elements andassociated electronics (shown in FIG. 4).

Overall, motor 500 may be a sensor-less, brushless, three-phase motor asdescribed above and illustrated in the various Figures. As shown, motor500 may include a stator 204, which may include three pairs ofelectromagnets. Each pair of electromagnets may have a correspondingpair of transistors, e.g., field effect transistors (FETs). Thetransistors may be configured such that each pair of electromagnets iseffectively bipolar, e.g., the polarity may be reversible. In otherwords, for each electromagnet pair, one transistor may drive the pair onthe high-side, or the other transistor may drive the pair on thelow-side. For example, FET 504 may be the high-side transistor for the‘U’ pair 302, while FET 506 may be the low-side transistor for the ‘U’pair of electromagnets 302. Similarly, FETs 514 and 516 may be therespective high-side and low-side transistors for the ‘V’ pair ofelectromagnets 304, while FETs 524 and 526 may be the respectivehigh-side and low-side transistors for the ‘W’ pair of electromagnets306. In addition to the particular embodiment shown, any number of otherwiring configurations (e.g. using a different number or types oftransistors) is also be possible and is contemplated.

The transistors for each pair of electromagnets may be controlled bydrive control logic 502. Drive control logic 502 may be electronic logicconfigured to perform various operations as described herein, such assampling voltages induced across the electromagnets, performingcalculations (e.g. simple integer math or more complex operations) todetermine values used for controlling the electromagnets, and/or sendingcontrol and/or power signals to the electromagnets. Drive control logic502 may also receive signals from one or more outside control devices,such as a fan speed control device. For example, a fan speed controldevice might periodically send an input command indicating a desiredchange in motor velocity based on some outside condition, such as anambient temperature, which drive control logic 502 might incorporateinto its control calculations. Other outside control devices are alsoenvisioned. Alternatively, such control devices may be incorporated intodrive control logic 502 itself.

In addition to any steady state or natural commutation control logicfunctions described herein, drive control logic 502 may have logic forcontrolling the motor under other conditions; for example, drive controllogic 502 may include logic for a DC excitation operation to align therotor to a known position prior to beginning rotation; logic for aforced commutation operation to begin rotation of the rotor; logic forstopping rotation of the rotor; logic for determining if a stallcondition exists; and/or logic for other functions, as well as logic forswitching from one function to another at an appropriate time.

Drive control logic 502 may be any of various types of logic, e.g.,analog or digital, or a combination thereof. For example, drive controllogic 502 may be implemented as a processor, e.g. a microcontroller,executing instructions comprised on a memory medium; a state-machinebased digital controller; a Field Programmable Gate Array (FPGA) and/ora mixed signal application specific integrated circuit (ASIC).Alternatively, drive control logic 502 may include any combination ofthe above. Drive control logic 502 may thus be implemented using any ofvarious digital or analog techniques, or a combination thereof, as wouldbe apparent to one of ordinary skill in the art.

As previously mentioned, motor 500 may be a brushless, three-phase motoras described above and illustrated in the various Figures. Motor 500 maythus be structured and may operate as motor 102 described in FIG. 2. Asteady state operation of motor 500 may be referred to as the naturalcommutation operation of the motor. Steady state or natural commutationmay refer to operation of a motor once the rotor is already spinning. Inother words, natural commutation may refer to maintaining or adjustingthe rotation speed of the rotor once it is already in motion. In someembodiments a motor may use a different method (e.g. different controllogic) for initiating rotation of a stationary rotor than it may use formaintaining or adjusting the rotation speed of an already rotatingrotor.

Three-phase brushless motors, such as motor 500, may be driven witheither sinusoidal or trapezoidal current waveforms. Classic driveschemes may rely on creating zero current switching in order to minimizethe effects of changes in instantaneous torque. These periodic changesin torque occur when the coils are energized and de-energized, orcommutated, producing mechanical vibrations and altering the inherentacoustic signature of the fan impeller. Both effects may be undesirablein many applications, including fans for the PC industry.

The effects of commutation on motor 500 may be minimized using asinusoidal current drive on each coil. This may be accomplished in oneof two ways, using a drive transistor as a linear pass device to createa sinusoidal current drive or to use a changing PWM duty cycle to createan effective sinusoidal current around each commutation point. However,each of these methods has some limitations. If a transistor is beingused as a pass element to generate a sinusoidal current in the coil, anyvoltage in excess of the voltage needed for sinusoidal waveformgeneration may constitute energy that is lost through dissipation.

Use of a changing PWM duty cycle to create an effective sinusoidalcurrent around each commutation point may not suffer from the losses ofa linear pass element, but it may consume additional current, as therewill be a minimum time when the current through any coil is zero. Thismay increase current consumption at any point where all three coils aredriven. In one set of embodiments, in order to minimize the effects ofthe coils switching, the “on” times and/or “off” times of drivetransistors in a full “H-bridge” drive scheme, such as the one shown inFIG. 5, may be delayed. That is, the respective “on” times and/or “off”times of transistor pairs 504 and 506, 514 and 516, and 524 and 526 maybe delayed such that the respective drive signals provided to theelectromagnets (and coils) between which the commutation occurs overlap.By overlapping the “on” times with respect to the commutation command orthe “off” times with respect to the commutation command, it may bepossible to minimize the effects of coils turning off. In addition tooverlapping the off-timing (or on-timing), the waveform of the currentconducted in the coils of the electromagnets may be shaped to minimizethe instantaneous rotational torque generated as the coil turns off. Theoverlap times may be controlled by digital timers, making the responsepredictable and easily controlled.

FIG. 6—Circuit Diagram of another embodiment of a Motor with DriveControl Logic

FIG. 6 illustrates a simplified circuit diagram of another embodiment ofa motor system 600. Motor system 600 may include motor 612 (which mayalso be similar to motor 102 shown in FIG. 2), and drive control logicthat includes a voltage divider circuit 602, a digitizer circuit 604, acalculation block 606, and a commutation engine 608. Motor 612 is drivenby driver block 610, which may include multiple driver stages, each ofwhich may be considered the corresponding driver stage of a respectivebuck regulator, with each driver stage including a respective pair oftransistors controlling an output voltage provided to a correspondingcoil of motor 612, and by extension the power provided to thecorresponding coil of motor 612. As shown in FIG. 6, drive transistorpair 614 a is configured to drive coil 616 a of motor 612, drivetransistor pair 614 b is configured to drive coil 616 b of motor 612,and drive transistor pair 614 c is configured to drive coil 616 c ofmotor 612. In this embodiment, the respective stator coils 616 a/b/c ofmotor 612 are used as the respective inductive elements that may be usedby the respective voltage regulators (e.g. buck style regulators, asmentioned above) for regulating the induced current provided to a load,to regulate the output voltage. In this case, while transistor pairs 614a/b/c may be used as the respective driving stages of correspondingvoltage regulators, the primary functionality of the regulators is toregulate the respective currents induced in coils 616 a/b/c, while theactual output voltage delivered to each coil may vary in time. Tocontrol the amount of current conducted by each coil, the desired valueof the control signal provided to the various transistor pairs 614 a/b/cmay be determined by calculation block 606 based on the input commandand motor rating (as previously described), and on the value of thevoltage rail obtained in real time through voltage divider 602 and railvoltage digitizer 604. The calculated value of the control signal (orrespective control signals) is then provided to commutation engine 608,which may generate the corresponding control signals for drivetransistors 614 a/b/c based on the calculated value obtained fromcalculation block 606.

Using the stator coils of motor 612 as the inductive elements forrespective voltage regulator(s), and calculating the drive signal, orrespective drive signals for stator coils 616 a/b/c according to (orbased on) the value of the rail voltage allows for a wide variation ofinput voltage (variation of high rail voltage) to motor 612, whilemaintaining a relatively constant output power to the motor 612. In theembodiments shown, the drive signal is a pulse width modulated (PWM)signal provided to transistor pairs 614 a/b/c, which may be operated asthe output driver stages of respective switching voltage regulator(s),e.g. a buck regulator(s). In this case, the value of the control signal,or each respective control signal, is the PWM duty cycle, or arespective PWM duty cycle, which corresponds to the PWM control signal,or respective PWM control signals generated by commutation engine 608.It should be noted, however, that different embodiments may usedifferent types of driver stages and/or corresponding voltageregulators, and in such embodiments the control signal, or respectivecontrol signals may be of a different type than a PWM signal. The mannerin which the value of the control signal, or respective control signalsis determined, as described herein, is independent of the type ofcontrol signal used, and may be used, more generally, to determine thedesired value of the control signal(s) to be provided to a respectivedrive stage or drive stages for powering the stator coils in the motor,in order to appropriately scale the maximum current through the statorcoils to the same magnitude that the coils would be expected to conductif the rail voltage were the rated fan/motor voltage, not the different,e.g. higher voltage rail to which the motor is actually coupled. Inother words, various embodiments of powering a rotating motor, e.g.motor 612 in FIG. 6, may include scaling the value of a control signalused for controlling power to the motor based on the value of the railvoltage, in addition to other factors, e.g. in addition to motor rating,and an input command indicative of a specified value of the controlsignal (which may simply be a previously determined value of the controlsignal).

It should also be noted, that as determined by the operation oftransistor driver stages 614 a/b/c connected as shown in FIG. 6, eachrespective output voltage provided to coils 616 a/b/c may have aspecific value determined by the high voltage rail, the transistordevices, and the voltage reference to which the bottom transistors arecoupled. Accordingly, adjusting the respective output voltages providedto coils 616 a/b/c in this case might refer to adjusting the time periodduring which the transistors are turned on and turned off, to controlhow long the specific voltage (close to high voltage rail when thetransistors are turned on, and close to the voltage reference when thetransistors are turned off) is provided to each coil. In alternateembodiments, depending on the method of power delivery to coils 616a/b/c, the output voltage may actually vary along an analog scale, andadjusting the output voltage in that case may result in variousdifferent voltage values provided to each coil.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

I claim:
 1. A method for controlling a rotating motor, wherein the motorcomprises a plurality of electromagnets, wherein each electromagnetcomprises a respective coil, the method comprising: measuring the valueof a supply voltage; receiving an input command to adjust a speed ofrotation of the rotating motor; determining and scaling the value of aduty cycle of a pulse width modulated control signal based on the inputcommand and on the measured value of the supply voltage; and generatingan output voltage adjusted to a motor rating in one or more of the coilsusing the control signal to obtain a desired value of the respectivecurrent, wherein the control signal controls two switching transistorswhose switching paths are coupled in series between the supply voltageand ground wherein a node between the switching paths is connected to acoil of the motor and wherein the switching transistor pair and the coilare operated as a buck voltage regulator.
 2. The method of claim 1,wherein said issuing an input command comprises: generating one or moretime values based on a representation of the angular velocity of therotating motor; and generating the input command based on the one ormore time values.
 3. The method of claim 1, wherein the duty cycle isfurther scaled based on a motor rating.
 4. A system comprising: anelectronic rotating motor, wherein the electronic rotating motorcomprises a stator comprising a plurality of electromagnets, whereineach electromagnet comprises a respective coil; a driver circuit poweredby a supply voltage, and configured to provide an output voltage derivedfrom the supply voltage to each of the plurality of electromagnets, toinduce a respective current in the respective coil of one or more of theplurality of electromagnets to generate respective induced currents; anda control block configured to adjust the value of each of the generatedrespective induced currents by pulse width modulation, wherein a dutycycle is adjusted based on an input command and the value of the supplyvoltage to adjust an angular velocity of the electronic rotating motor,wherein the control block is further configured to obtain one or moretime values based on a representation of the angular velocity of theelectronic rotating motor determined by the induced respective currents,and generate the input command based on the one or more time values. 5.The system of claim 4, wherein the control block is further configuredto generate one or more control signals based on the input command andthe value of the supply voltage, and adjust the value of each of thegenerated respective induced currents by controlling the one or more ofthe plurality of electromagnets with the one or more control signals. 6.The system of claim 4, wherein the driver circuit comprises for eachmotor coil two switching transistors whose switching paths are coupledin series between the supply voltage and ground wherein a node betweenthe switching paths is connected to a respective coil of the motor andwherein each switching transistor pair and associated coil are operatedas a buck voltage regulator.
 7. The system of claim 6, wherein thesupply voltage is higher than a rated voltage for said motor.
 8. Asystem for controlling an electronic motor that comprises a plurality ofelectromagnets, wherein each electromagnet comprises a respective coil,the system comprising: a driver circuit powered by a supply voltage, andconfigured to provide an output voltage derived from the supply voltageto each of the plurality of electromagnets, to induce a respectivecurrent in the respective coil of one or more of the plurality ofelectromagnets to generate respective induced currents; and a controlblock configured to adjust the value of each of the generated respectiveinduced currents by pulse width modulation, wherein a duty cycle isadjusted based on an input command and the value of the supply voltageto adjust an angular velocity of the electronic motor, wherein thecontrol block is further configured to determine one or more time valuesbased on a representation of the angular velocity of the electronicmotor determined by the induced respective currents, and generate theinput command based on the one or more time values.
 9. The system ofclaim 8, wherein the control block is further configured to generate oneor more control signals based on the input command and the value of thesupply voltage, and adjust the value of each of the generated respectiveinduced currents by controlling the one or more of the plurality ofelectromagnets with the one or more control signals.
 10. The system ofclaim 8, wherein the driver circuit comprises for each motor coil twoswitching transistors whose switching paths are coupled in seriesbetween the supply voltage and ground wherein a node between theswitching paths is connected to a respective coil of the motor andwherein each switching transistor pair and associated coil are operatedas a buck voltage regulator.
 11. The system of claim 10, wherein thesupply voltage is higher than a rated voltage for said motor.
 12. Amethod for controlling a rotating motor, wherein the rotating motorcomprises a plurality of electromagnets, wherein each electromagnet ofthe plurality of electromagnets comprises a respective coil, the methodcomprising: inducing a respective current in one or more of therespective coils, by providing respective output voltages derived fromat least one rail voltage to the one or more respective coils; receivingan input command to adjust the respective values of one or more pulsewidth modulated control signals used for adjusting a speed of rotationof the rotating motor; scaling duty cycles of the one or more pulsewidth modulated control signals based on the input command and ameasured value of the at least one rail voltage to adjust each inducedrespective current to a desired respective value representative of amaximum current that the one or more respective coils are expected toconduct for a specified value of the rotating motor, wherein thespecified value of the rotating motor is different from the measuredvalue of the of the at least one rail voltage.
 13. The method of claim12, wherein the measured value of the at least one rail voltage ishigher than the specified value of the rotating motor.
 14. The method ofclaim 12, wherein said scaling the respective values of the one or morecontrol signals comprises: sensing a value of the at least one railvoltage; digitizing the sensed value of the at least one rail voltage toobtain a numeric value representative of the present value of the atleast one rail voltage; calculating respective desired values of the oneor more pulse width modulated control signals according to the inputcommand and the numeric value representative of the sensed value of theat least one rail voltage; and adjusting the respective values of theone or more pulse width modulated control signals to the correspondingrespective desired values.
 15. The method of claim 12, wherein saidproviding the respective output voltages comprises providing therespective output voltages through respective switching voltageregulators wherein each coil of the rotating motor is part of arespective switching voltage regulator.
 16. The method of claim 15,wherein said scaling the respective values of the one or more controlsignals comprises scaling the respective duty cycles of respective pulsewidth modulated control signals provided to the respective switchingvoltage regulators.
 17. A system comprising: an electronic rotatingmotor, wherein the electronic rotating motor comprises a statorcomprising a plurality of electromagnets, wherein each electromagnetcomprises a respective coil; a driver circuit powered by a supplyvoltage, and configured to provide an output voltage derived from thesupply voltage to each of the plurality of electromagnets, to induce arespective current in the respective coil of one or more of theplurality of electromagnets to generate respective induced currents; anda control block configured to adjust the value of each of the generatedrespective induced currents by pulse width modulation, wherein a dutycycle is adjusted based on an input command and the value of the supplyvoltage to adjust an angular velocity of the electronic rotating motor;wherein the driver circuit comprises for each motor coil two switchingtransistors whose switching paths are coupled in series between thesupply voltage and ground wherein a node between the switching paths isconnected to a respective coil of the motor and wherein each switchingtransistor pair and associated coil are operated as a buck voltageregulator.
 18. The system of claim 17, wherein the supply voltage ishigher than a rated voltage for said motor.